An apparatus effecting continuous flushing of intravascular catheters in systems for monitoring conditions in the thoracic cavity during surgery in the intensive care ward, cardio vascular diagnostic laboratories, etc. The apparatus embodies a small block having therein passages for a flushing solution in one of which is a flow resistor to limit the flushing to a small amount, a fail-safe valve in another passage connected by a bypass to the first passage for fast flushing with a much larger amount of solution, and means for connecting the catheter to a monitoring apparatus.

Quinn ..25l/333 R X Hall et al.. ..25l/l 17 Langdon ..251/38 Bergman ..,.128/2l4 R Primary Examinerl-lenry T. Klinksiek Attorney-Hill, Sherman, Meroni, Gross & Simpson 57 ABSTRACT An apparatus effecting continuous flushing of intravascular catheters in systems for monitoring conditions in the thoracic cavity during surgery in the intensive care ward, cardio vascular diagnostic laboratories, etc. The apparatus embodies a small block having therein passages for a flushing solution in one of which is a flow resistor to limit the flushing to a small amount, a fail-safe valve in another passage connected by a bypass to the first passage for fast flushing with a much larger amount of solution, and means for connecting the catheter to a monitoring apparatus.

10 Claims, 5 Drawing Figures CONTINUOUS CATHETER FLUSI-IING APPARATUS SUMMARY OF THE INVENTION Catheter cannulation of an artery or a vein for pressure monitoring, particularly of central pressure in the thoracic cavity, has become an indispensable technique in modern hospitals. For example, from a central arterial catheter introduction system and a continuous and intemiittent flush system which allow high quality clinical recording of central arterial pulse waveforms, it is possible to measure a number of parameters from the central pulse contour. Such parameters include stroke volume, heart rate, cardiac output, duration of systole, and systolic, diastolic and mean pressures. In addition, blood for intermittent arterial blood gas analysis can be withdrawn.

It has been found necessary to continuously flush the catheter to prevent occlusion of the intravascular catheter end by blood clotting, and maintain catheter patency for continuous recording over periods which may amount to several days. Continuous flushing systems utilizing marine-bore capillary tubes as flow resistors and applying the flushing solution under pressure have heretofore been devised, one such being described in an article appearing on pages 675-678 of the Journal of Thoracic and Cardiovascular Surgery, Volume 57, No. 5, May, 1969. Formerly known systems for the intended purposes embodied an objectionably large amount of apparatus complicated to set up and these former systems presented a major problem in maintaining a high quality of pulse waveform. That resulted in a loss of fidelity of recording due to clots and high viscosity blood being in the catheter system, and the largest contributor to this problem was stopcocks, a number of which were used in every prior system of which we are aware. Stopcocks have minute leaks, and although great pains were taken to maintain high quality stopcock integrity, it was found that that was almost impossible to achieve in practice. Even with a perfect stopcock system there is still a small volume displaced with each pressure pulse, and, therefore, a small amount of blood enters the catheter tip with each pressure pulse, and evenwith a perfectly tight system it was virtually impossible to keep blood out of the tip of the catheter. Blood once entering the tip of the catheter, can then, by a process of diffusion, penetrate further and further into the catheter and finally an occlusion results and pressure pulse fidelity decreases. Further, if the system were to be filled in a reasonable time, which is essential before operation can begin, an additional stopcock and fluid source was required.

The instant invention overcomes the foregoing deficiencies in the provision of a small unitary piece of apparatus for connection in the catheter flushing system and which is so constructed so as to eliminate the use of all stopcoc-ks in that flushing system. The instant invention includes a resilient valve controlling a bypass around the flow resistor and this valve is leak-proof, fail-safe, and quick acting and permits the measurement of dynamic characteristics of a catheter transducer system, that is, allowing fast shut-off for square wave testing of a catheter system on an oscilloscope or the like. With this simple form of structure, much of the apparatus along with a complicated setup, heretofore required, has been eliminated. Consequently, with the instant invention, it is possible to monitor the central arterial pulse waveform with its various derived parameters with much greater ease, flexibility, and accuracy than was heretofore possible. The reliability of the pressure measuring system has been increased and the competence 'of the nurses, physicians and auxiliary personnel in determining the patients vital signs and conditions from the central arterial waveform have also been materially increased.

Other objects, features and advantages of the invention will be readily apparent from the following description of a preferred embodiment thereof, taken in conjunction with the accompanying drawing although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure.

FIG. 1 is a diagrammatic disclosure illustrating a device embodying principles of the instant invention in operative association with a catheter cannulated patient and a source of flushing solution, the device itself being exaggerated in the showing for purposes of clarity;

FIG. 2 is an enlarged central vertical sectional view through the device itself, with the valve in closed position;

FIG. 3 is a transverse sectional view taken substantially as indicated by the line III-III of FIG. 2;

FIG. 4 is a plan sectional view taken substantially as indicated by the line IV-IV of FIG. 2; and

FIG. 5 is a view similar to FIG. 2 but showing the valve in open position.

DETAILED DESCRIPI'ION'OF THE PREFERRED EMBODIMENT While the instant invention may be incorporated in various catheter systems and even in certain other systems for the purpose of governing flow through the system, and is highly useful in systems for monitoring venous and arterial pressures, by way of example, the system is shown and will be described herein with regard to a catheter system for. monitoring central arterial pressure and permit high quality clinical recording of central arterial pulse waveforms. The catheter used in such a system is a thin catheter having an inside diameter in the neighborhood of one-half a millimeter and which is preferably made of polytetrafluoroethylene. Such a catheter must be kept patent during use by preventing the formation of a blood clot or other occlusion at the body end of the catheter and sufficient infusion solution must be continuously passed through the catheter for that purpose, but not in such amount as to be harmful to a patient during a relatively long period of monitoring. It has been detennined that in the case of an infant 1 cc. of infusion solution per hour is sufficient, and in the case of an adult 2 to 3 cc. per hour of solution is sufficient. Accuracy of the system must therefor be insured at all times, but at the same time means must be provided to establish a rapid flush in the first instance to clear out the system of all air and till the system quickly, and a rapid flush is necessary from time to time to check the dynamics of the entire system in a manner to avoid deceiving the observer and confusing the records.

With the foregoing in mind, in FIG. 1 we have given a diagrammatic showing of a control device I embodying principles of the present invention installed in a system for monitoring cardiovascular pressure. The overall system includes a pressurized infusion container 2 connected by a tube 3 to a micron filter 4 which prevents clogging of the flow resistance element to be later described and eliminates bacteria that may be in the infusion solution, the filter being connected to one end of a tube 5, the other end of which is securely afiixed in the device 1. The device is also provided with a fitting 6 to which the catheter 7 is connected. In the illustrated showing the catheter is advanced into the thoracic cavity of a patient 8 by way of entrance into the radial artery. Another fitting 9 is provided on the device I for connection to an indicating mechanism such as a manometer, as diagrammatically indicated at 10, or to a pressure transducer associated with an oscilloscope, or the fitting may be equipped with a self-sealing plug for hypodermic injection in case such becomes indicated. It will be understood that the instant invention is usable in catheter systems wherein the catheter may be entered into various veins or arteries of the body. a

The device 1 may be fabricated of several parts molded of rigid plastic material, preferably transparent, and the parts may be secured together cementitiously, by fusing or welding, with the use of a solvent, or in any other suitable manner. In the illustrated showing the device consists of a housing in the form of a block composed of a body 11, an end cap 12 carrying the catheter fitting 6, and an opposite end cap 13 carrying the fitting 9 as well as other points of entry into passages in the body. When it is considered that the body and end caps, exclusive of the fittings 6 and 9, may be sized as little as seveneighths inch long, three-quarter inches wide, and one-quarter inch thick, the advantage of the instant invention in eliminating apparatus utilized herebefore, including all stopcocks, in providing an easily connectable structure and one which may be suspended from the tubing since it weighs extremely little, and performs all the above desired operations in controlling flow through the system, will be at once appreciated.

The body 11 is molded to provide a passage 14 connecting the hollow fittings 7 and 9, the fitting 9 being internally shaped as indicated at 15 to provide a connection for a Luer fitting. Another and larger passage 16 is provided in the body 11 and cap 13 and this passage communicates with a cross-passage 17 by way of a reduced outlet opening 18, the passage 17 connecting at one end with the aforesaid passage 14. Still a further passage 19 is provided in the body 11 and the inner end of the passage 19 tapers inwardly to a reduced size 20 and establishes a valve seat at 21, the reduced passage 20 also communicating with the cross-passage 17. Along the side of the passage 19 nearest the passage 16 a small bypass passage 22 is provided in open communication with the passage 19 and this passage connects with the passage 16 by way of a side branch 22. The aforesaid tube 5 for connection to the infusion system has its end portion permanently connected inside the passage 16, the cap 13 being provided with a stop element 23 thereon to prevent the tube from blocking the branch passage 22 when the tube is initially being assembled to the cap 13.

Within the passage 16 is a flow resistance in the form of a tube 24 having a resilient apertured sealing washer 25 at each end thereof. The resistance 24 is what is referred to as a marine-bore tube and the actual bore 26 through the tube is but several hundredths of a millimeter in diameter so as to afford a high resistance to the flow of infusion solution through the resistance element. It will be appreciated that the showing in the drawing is highly exaggerated insofar as the instant invention is concerned for purposes of clarity since the bore 26 in the tube 24 is virtually invisible to the naked eye when gazing at an end ofthe tube.

The capillary tube 24 with its minute bore 26 provides a high resistance to flow therethrough. An increase or decrease in the length of tube 24 will decrease or increase the rate of flow in a linear fashion. Since this flow is laminar, Poiseuilles law is applicable, and therefore small variations in the radius of the bore 26 in the resistance tube will cause relatively large variations in the amount of flow. In calculating flow through the system, not only the resistance afforded by the tube 24 must be considered, but the resistances of the catheter and the filter 4 must also be taken into consideration. Those resistances are known, that of the catheter being relatively high, namely about eighty millimeters of mercury per cubic centimeter per minute, and that of the 0.22 micron filter is millimeters of mercury per cubic centimeter per minute. By way of example, using a resistance tube having a bore of a diameter of 0.05 millimeter and a length of l centimeter, with 300 millimeters of mercury pressure on the infusion solution source 2 a flow of 3 cubic centimeters per hour is obtained, and the effective resistance of the infusion system would be about 6,000 milli-meters of mercury per cubic centimeter per minute. Back pressure from the patients body has no adverse effect on the flow, and a flow of about 3 cubic centimeters per hour will constantly flush the catheter to avoid any occlusion therein, and will not interfere with or lessen the high quality of the clinical recording of the central arterial pulse waveforms.

Obviously, to initially fill the system by way of such a small flow through the resistance tube would require an objectionable amount of time. To that end, means are provided in the passage 19 to provide for a rapid flushing or quick filling of the entire system. Such means comprise a valve 27 of resilient material, such as rubber or synthetic rubber, which seats on the seat 21. The valve has a cylindrical extension 28 extending from the valve body and the outer end of this extension is seatingly engaged over aninwardly extending nipple 29 on the cap 13. The length of the valve body and extension 28 is slightly greater than the distance from the valve seat to the cap 13 so that the valve is sealed against its seat under its own pressure and blocks any bypassing of solution through the passages 20 and 21. The valve is actuated manually by means of a valve stem 30 extending from the valve body through the extension and through the cap 13. When that valve stem is manually pulled outwardly the valve is drawn away from the seat 21 opening the bypass and the extension 28 of the valve will assume a corrugated effect as indicated at 31 in FIG. 5. The structure of the valve makes it fail-safe, in that it cannot accidentally be left in open position because when the stem 30 is released the valve will automatically and forcefully close quickly. The valve will also seat accurately because of a guiding projection 34 extending from the valve body into the smaller passage 20.

In use, the flow control device 1 is extremely efiicient. Prior to the insertion of the catheter in the patients body, but after the connection of the device 1 to the pressurized infusion solution source, the stem of the valve 30 is pulled to open the valve and flush out the system including the catheter so as to eliminate any possible air bubbles. During such flushing infusion solution will follow the line of arrows 32 through the bypass passageways and out the fitting 6. The valve is closed after the initial flushing out, but the catheter may be inserted in the patients body while the flow flushing infusion through the resistance tube 24, as indicated by the arrows 33 in FIG. 2, continues. The fitting 9 is, of course, connected to whatever indicating or recording means may be desired, or to a pressure transducer for oscilloscopic observations, and the catheter will be maintained patent throughout a long interval of time. It is essential for assuring waveform quality to determine the dynamic response of the entire system from time to time. This is simply accomplished by opening the valve 27 and permit it to quickly close. Such a rapid flush will cause what is termed a square wave to appear on an oscilloscope and such will not mislead the observer nor will it confuse any permanent record. The valve is amply rapid in its action to perform that function.

During the use of the instant flow control and flushing device 1, there can be no backflow because the blood pressure of the patient is insufficient to force liquid through the capillary tube 24 in the reverse direction. The device is extremely light in weight, highly efiicient as to its functioning, eliminates complicated setups of apparatus, and makes it possible to monitor the central arterial pulse waveform with its various derived parameters with much greater ease, flexibility and accuracy than was heretofore possible. Also, the device is sufficiently economical to warrant its disposition along with the catheter after a single usage, if such may be indicated, although the device may be repeatedly used, sterilized if deemed necessary, if the conditions of the patients permit.

What we claim is:

1. A continuous flow control apparatus highly desirable for use in a liquid flow system for pressure monitoring of hemodynamics, such system including a catheter which must be kept patent by continuous flushing when in use, comprising a block having passages therein defining continuously open inlet-outlet path through the block,

a flow resistor in the form of a marine-bore capillary tube in said path to limit flow of liquid under pressure therethrough to a desired minimum amount,

said block having other passages therein defining a by-pass around the pan of said path containing said resistor which by-pass is of a size to permit a fast flow of liquid,

said by-pass being interiorly shaped to provide a valve seat,

and

a resilient valve means having a stem projecting out of said block positioned in said by-pass and so mounted as to forcefully press against said valve seat and automatically and instantaneously close when said stem is released.

2. The apparatus of claim 1 wherein said block is less than 1 inch in any direction and sufficiently light in weight to be suspended in a fluid line.

3. The apparatus of claim 1, including a flexible tube anchored at one end in said path, and

a fitting on the other end of said tube for connection to a pressurized fluid source.

4. The apparatus of claim 1, wherein said valve comprises a solid body shaped to fit against said valve seat, and

a tubular extension on said body sealed at its outer end and which is compressible when the valve is opened.

5. The apparatus of claim 1, including a hollow nipple projecting from said block into said by-pass at the end opposite said valve seat, and

said valve comprises a solid body shaped to fit against said valve seat, and

a tubular extension on said body sealed around said nipple and which is compressible to open said valve.

6. The apparatus of claim 5, wherein said valve and extension are slightly longer than the space occupied whereby there is continuous pressure urging the valve against said seat, and

said stem extends from the valve body through said extension for actuating said valve.

7. The control apparatus of claim 6 wherein said valve body,

extension and stem are all integral.

8. The control apparatus of claim 1, wherein said block has a passage therethrough with one end thereof in communication with the outlet end of said path, and

a fitting at the other end of the last said passage for connection to monitoring means or to be plugged for hypodermic injection.

9. The'control apparatus of claim 1, wherein said resistor is sized to permit a flow not exceeding 4 cubic centimeters per hour.

10. The control apparatus of claim 1, wherein said by-pass narrows at one point to form said valve seat,

and

a guide projection on said valve extends through the valve seat into the narrower part of said by-pass to insure accurate seating of the valve.